Due to its characteristics of being easily applicable to various products and electrical characteristics such as a high energy density, a secondary battery is not only commonly applied to a portable equipment, but universally applied to an electric vehicle (EV), a hybrid vehicle (HV), or an energy storage system that is propelled by an electric motor. This secondary battery is gaining attention for its primary advantage of remarkably reducing the use of fossil fuels and not generating by-products from the use of energy, making it a new eco-friendly and energy efficient source of energy.
A battery pack for use in electric vehicles has a structure of a plurality of cell assemblies including a plurality of unit cells are connected in series to ensure a high output. Also, the unit cell can be charged and discharged repeatedly by an electrochemical reaction between elements including a cathode current collector, an anode current collector, a separator, an active material, an electrolyte solution, and the like.
In addition to this basic structure, the battery pack further includes a battery management system (BMS) to monitor and control a state of a secondary battery by applying an algorithm for control of power supply to a driving load such as a motor or the like, measurement values of electrical characteristics such as current, voltage, and the like, charge/discharge control, voltage equalization control, state of charge (SOC) estimation, and the like.
Recently, with the increasing need for a high-capacity structure as well as utilization as an energy storage source, the demand for a battery pack of a multi-module structure in which a plurality of battery modules including a plurality of batteries connected in series and/or in parallel are assembled, is also increasing.
Because the battery pack of the multi-module structure includes a plurality of batteries, there is a limitation in controlling the charge/discharge state of all the batteries using a single BMS. Accordingly, a recent technology has been introduced in which a BMS is provided to each battery module included in the battery pack, designates any one of the BMS as a master BMS and the remaining BMSs as a slave BMS, and controls the charge and discharge of each battery module in a master-slave mode.
The slave BMS stands by in a sleep mode during a normal state, wakes up by a wake-up signal from the master BMS, and is allocated with an identifier from the slave BMS.
Although the wake-up signal can be transmitted through various communication networks, generally, a serial communication network is mainly used. The serial communication network has advantages of easily implementing a communication configuration, having excellent signal transmission characteristics, and allowing an existing communication line to be used, leading to significant reduction in costs.
The serial communication network has a connection scheme in which a receiver receiving a signal becomes a transmitter and relays the signal to an adjacent receiver connected to the receiver. Accordingly, when an error or a disconnection occurs in a certain section of the serial communication network, signal transmission fails from the faulty communication section.
Accordingly, in a case of a battery pack including a plurality of slave BMSs connected through a serial communication network, when an error or a disconnection occurs in a certain section of the communication network, some slave BMSs do not wake up and cannot be allocated with an identifier. Particularly, the closer the faulty section of the communication network is to a master BMS, the greater the number of slave BMSs that do not wake up increases. In this case, the master BMS cannot communicate with a slave BMS having no allocated identifier, and thus, cannot recognize the charge/discharge state of a battery cell or a battery module included in the slave BMS having no allocated identifier. As a result, a total capacity of the battery pack may be reduced, or further, the use of the entire battery pack may be stopped.